Thermoporoelastic properties of Flechtinger sandstone

This research addresses the thermomechanical response of a saturated sandstone in a geothermal reservoir. Several experiments were performed using a triaxial testing system to investigate thermal effects on poroelastic parameters of Flechtinger sandstone, an outcropping equivalent of the (Rotliegend) reservoir rock. In drained experiments, confining pressure was cycled, pore pressure was maintained constant and temperature was increased step-wise. The temperature dependence of the drained bulk modulus differed at low and high effective pressures. The unloading drained bulk modulus increased from 10.25 GPa to 11.74 GPa with increasing temperature from 30 °C to 120 °C at high stresses and decreased from 3.39 to 3.05 GPa at low stresses. The Biot coefficient decreased with increasing effective pressure and temperature. The inelastic behavior of the rock, the interrelation between thermal expansion coefficient and bulk modulus, and the path dependence of heat transfer processes govern the temperature effect on granular rock and changes in pore geometry.

► Temperature effects and changes in pore geometry result in nonlinearity.
► The temperature effects differ at low and high stresses.
► The interrelation between thermal expansion coefficient and bulk modulus is prevalent.
► The Flechtinger sandstone suffered permanent deformation and inelastic behavior.